The invention relates in general to manual die sets for pressing explosive powder and in particular to a self-aligning manual die set for pressing explosive powder into pellets.
Manual die sets for pressing explosive powder into pellets are known. The explosive powder is a highly sensitive explosive molding powder, for example, PBXN-9 or PBXW-11. The manual die set, in combination with a press for supplying the pressing force, presses the explosive powder into solid cylindrical pellets.
FIG. 1 is an elevation view, partially in cross-section, of a known manual die set 10 in a press configuration and FIG. 2 is an elevation view, partially in cross-section, of the known manual die set 10 of FIG. 1 in a knockout configuration. Manual die set 10 includes a die 12 with an opening 14 therethrough, a ram 16 having a head 18, a baseplate 22 that fits in the bottom of the opening 14 in die 12 and a knockout ring 24.
Manual die set 10 is used to press highly sensitive explosive molding powder 20 into a pressed pellet 26 in the following manner. First, the baseplate 22 is fitted into the opening 14 in the bottom of the die 12. The required amount of molding powder 20 is poured into the die opening 14. Next, the ram 16 is inserted into the top of the die opening 14 and allowed to "float" down as its weight forces air out of opening 14. Air escapes through the limited clearance between the ram 16 and the die wall until the ram 16 rests on the surface of the powder 20.
Next, the die set 10 is placed under a pressing mechanism (not shown), such as a hydraulic ram, and press force is applied to the ram head 18 for a required dwell time. After pressing, the die set 10 is lifted and placed on top of the knockout ring 24. If the baseplate 22 is loose, it is usually removed before the die is placed on the knockout ring 24. Finally, the ram 16 is pressed completely down, ejecting the baseplate 22 (if not previously removed) and the pressed pellet 26 into the cavity in the knockout ring 24. Usually, a small piece of wadding or foam rubber (not shown) is inserted in the bottom of the knockout ring 24 to cushion the landing of the baseplate 22 and/or pellet 26.
FIG. 3 is an elevation view, partially in cross-section, of the manual die set 10 of FIG. 1 showing an alignment problem. The amount of misalignment shown in FIG. 3 is somewhat exaggerated to illustrate the problem. While pressing pellets using the manual die set 10, it is difficult to align the ram 16 vertically in the die 12. Also, the ram 16 may become cocked in the die 12 when the pressing pressure builds up. The lack of vertical alignment causes a high shear stress area 17 with safety problems where the edge of the ram 16 touches the die wall. First, the ram 16 may cause galling of the interior wall of the die 12, requiring replacement of the die. Second, the ram 16 may pinch some of the powder 20 against the die, which may cause an explosion. Third, as the pellet 26 is ejected, the ram 16 can shear off the explosive residue on the inside surface of the die 12, resulting in an explosion. These are serious safety problems when pressing highly sensitivity explosive molding powder.
Thus, a need exists for a manual die set that overcomes the problems of the manual die set of FIGS. 1-3.